Process for the determination of the deep drawing quality of sheet material



July 7, 1964 J. H. ZAAT PROCESS FOR THE DETERMINATICN OF THE DEEP DRAWING QUALITY OF SHEET MATERIAL Filed May 17, 1961 United States Patent PROCESS FQR THE DETERMINATION OF THE DEEP DRAWING QUALITY OF SHEET MATERIAL Johannes Huhertus Zaat, Delft, Netherlands, assignor to Nederlandse Organisatie voor Toegepast-Natuurwetenschappeliilr Onderzoek ten Behoeve van Nijverheid, Handel en Verkeer, The Hague, Netherlands, a corporation of the Netherlands Filed May 17, 1961, Ser. No. 110,621 Claims priority, application Netherlands May 23, 1960 6 Gaines. (Cl. 73-87) The invention relates to a process and set of tools for the determination of the deep drawing quality of sheet material, particularly metal, in which circular discs of this material are formed into cylindrical or substantially cylindrical cups by means of deep drawing tests and in which the ratio between the dimensions of the discs-a certain percentage of which has caused rupture during deep drawing--and the diameter of the punch is determined.

Frequently, in this process that ratiolimiting drawing ratio-between the disc diameter and the punch diameter is chosen, which will lead to rupture in a small percentage of the cups. This ratio is then used as a measure for the deep drawing quality, but because of the choice of the percentage it is often arbitrary.

In many cases the result is unreliable because the tool dimensions, the testing conditions combined with the sheet thickness, and the properties of the material play a very important part.

In order to obtain useful data concerning the properties of the material, all the other influences were kept as constant as possible.

It was thought that good results could he arrived at, if all the dimensions and conditions had been established and were kept constant.

However, the drawback made itself felt that the knowledge of the properties was tied down to the sheet thickness of the material; usually metal, and to the diameter of the punch; and that tests with the same material but various thicknesses or tests with equal thicknesses but various punch-diameters, ended in different results.

The object of the invention is to provide a process and set of deep drawing tools for the determination of the deep drawing quality of metals, in which a certain liberty in the choice of tool-dimensions and drawing-conditions is present, without the workableness and the comparability of the results being adversely influenced thereby, so that sheets of various thicknesses can be compared as to their deep drawing properties, and so that for one and the same sheet thickness the dimension scale is eliminated, so as to make it possible to predict the drawing properties of the larger products of the same thickness to be made in a factory.

Reference is now made to the accompanying drawing showing a schematic of the tools involved, wherein numeral 1 represents the tool die, 2 the punch, 3 the sheet material to be drawn, and 4 suitable holding means having a load force H. It is of course understood that suitable actuating means for the punch and other associated apparatus are available.

To achieve this, it is a feature of the invention that in each test each of the parameters each time has the same or substantially the same value, whereby D =die boring diameter, D =punch diameter,

r =die edge radius,

r =punch edge radius,

t =sheet thickness,

C =clearance parameter, C =punch edge radius parameter, C =die edge radius parameter.

Now if a limiting drawing ratio T is defined as the ratio of the limiting blank diameter D, of the circular disc which is formed into a cup, to the sum of the punch diameter D, and the sheet thickness to:

Dk t .T

while the limiting blank diameter D, is that diameter of the disc, at which a certain percentage, for instance 50% of the products, is ruptured and can, therefore, not be drawn further into a cup, then it appears that this limiting drawing ratio is highly independent of the choice of certain dimensions, such as the sheet thickness t and the punch diameter D The result of the tests will also be influenced by the magnitude of the blankholder load; It is known per se that a constant blankholder force as well as a constant pressure per unit of surface exercise an influence on the results, when one or more dimensions such as the sheet thickness t and the punch diameters D are varied.

Therefore, a further feature of the invention is that the blankholder load is proportional to the sheet thickness 1 and to the difference between the die diameter and the sheet thickness, and to a proportionality factor C i.e. H=C .t (D This may be rewritten as H o(- m o) It appears that, if these conditions are fulfilled, the blankholder load H exerts no perceptible irrfiuence on the measuring results, if the parameters C C and C remain the same.

Although the choice of the numerical value of the parameters is practically free, it is only natural that in making this choice the practical possibility of these tests should be taken into account, which might be endangered when extreme values were chosen for the parameters.

Therefore, according to the invention the value of the parameter C lies between 1 and 1.2 and that of the parameters C, and C between 1 and 20.

In the practical realization it is naturally impossible to keep the parameters C C and C entirely constant for all the tools and the sheet-thicknesses to be used. If, however, it is desired to keep down the influence which the variation in value of the parameters has on the measuring results of T for instance below 1%, then the value of C may deviate by at most 1%,. that of C by at most 0.02 C, and that of C by at most 3% from the values chosen.

In connection with the above, it is preferred to choose the following values for the parameters.

and

For the composition of such a set of tools it is preferably started from at most two punch diameters; the remaining dimensions of the tools are determined by the choice of the numerical value of the parameters, by the thicknesses of the metal sheets used for the tests and by the accuracy standard imposed in these tests. An

example of such a set of tools is rendered in the following table.

to DB 15 Dm m 0. 34-0. 39 25.00 2. 36 25. 59 2v 5 0. 39-0. 46 25. 2. 36 2e. 09 2. 9 0. 45-07 52 25. 00 2. 25 26. 94 3. 4 0. 52-0. 59 25. 00 2. 26 25. 94 3. s 0. 59-0. 71 25.00 2. 26 27. 20 4. 5 0. 71-0. 34 25. 00 2.16 27. 46 5. 4 0. 84-0. 97 25. 00 2.16 27. 71 6. 3 07 68-0. 80 50.00 4. 73 53.38 5. 1 0.80-0.93 50.00 4. 73 53.38 6.0 0. 93-1. 04 50.00 4. 53 53.89 6.8 1. 04-1. 18 50.00 4. 53 53.89 7. 7 1.18-1.43 50. 00 4. 53 54. 40 9. 1 1. 43-1138 50.00 4. 32 54. 91 10. 8 1. 68-1. 94 50.00 4. 32 55. 43 12. 6

I claim:

1. A method of determining the deep drawing quality of sheet materials comprising the steps of: selecting a circular disc of the sheet material having a thickness t placing the disc on a die defining a circular bore of diameter D said die having a radius R at the edge of the die at the bore, selecting a cylindrical punch having the diameter D and the radius R at the edge of the punch at one end thereof, and drawing the disc through the die bore with the punch at the said one end to form a substantially cylindrical cup, and repeating the steps with other circular discs of the sheet material such that remains substantially constant throughout the method, and wherein C represents the clearance parameter, C represents the punch edge radius parameter and C represents the die edge parameter.

2. The method according to claim 1 and further comprising the step of applying a load H to hold the disc against the die before drawing, and wherein the ratio 7 H o( m o) remains substantially constant.

3. The method according to claim 2 wherein the substantially constant values of C C and C are selected from the ranges of l to 1.2, l to 20 and l to 20, respectively and the i variations of each value are 1%, 0.02 G and 3% respectively.

4. A method according to claim 3 wherein the values of C C and C are 1.035i1%, 7:10% and 513%, respectively.

5. A method according to claim 1 wherein the quality of deep drawing is determined by the limiting drawing ratio wherein D; is a diameter of the disc.

6. The method according to claim 5 wherein D; is the diameter at which one-half of the discs rupture after drawing.

References Cited in the file of this patent UNITED STATES PATENTS 2,875,608 Engelhardt et al. Mar. 3, 1959 FOREIGN PATENTS 872,403 Germany Mar. 30, 1953 1,079,588 France May 19, 1954 

1. A METHOD OF DETERMINING THE DEEP DRAWING QUALITY OF SHEET MATERIALS COMPRISING THE STEPS OF: SELECTING A CIRCULAR DISC OF THE SHEET MATERIAL HAVING A THICKNESS TO, PLACING THE DISC ON A DIE DEFINING A CIRCULAR BORE OF DIAMETER DM, SAID DIE HAVING A RADIUS RM AT THE EDGE OF THE DIE AT THE BORE, SELECTING A CYLINDRICAL PUNCH HAVING THE DIAMETER DS AND THE RADIUS RS AT THE EDGE OF THE PUNCH AT ONE END THEREOF, AND DRAWING THE DISC THROUGH A SUBSTANTIALLY CYLINDRICAL CUP, AND REPEATING THE STEPS WITH OTHER CIRCULAR DISCS OF THE SHEET MATERIAL SUCH THAT EACH PARAMETER 